1. Field of the Invention
This invention relates to the field of network communications. In particular, the present invention relates to an efficient system and method for signal spectrum spreading and combining into a single stream.
2. Related Art
Electronic devices and systems have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. These advantageous results are often realized and maximized through the use of distributed resources (e.g., a personal computer, video device, telephone, etc.) that rely on information communicated over a network in the performance of their prescribed tasks (e.g., internet interface, movie presentation, or communication of a conversation). The information is typically communicated in accordance with predetermined protocols. The ease and efficiency at which the information is converted between communication protocols and processing configurations often has a significant impact on the performance of the end use devices.
There are numerous different communications networks that transfer information in a variety of implementations. Typically a network is defined by its attributes and abilities such as the type of communication medium used (e.g., copper wires, fiber optics, coax cable, radio waves, microwaves, etc.), the cable layout (or topology), data transfer rates, communication protocols, and the method used by nodes to access and use the network (access methods). Usually there are a number of end use devices (e.g., personal computers, telephones, etc.) that are coupled together by communication mediums which convey information to a destination with the assistance of intermediate control devices (e.g., bridges, routers, gateways, switches, repeaters, cellular base stations, satellites, etc.). Wireless communications typically offer a variety of benefits including portability and ease of use. In particular, Code Division Multiple Access (CDMA) digital cellular wireless communication protocols have emerged to typically offer greater signal quality than other wireless communication protocols (e.g., Time Division Multiple Access (TDMA)) resulting in clearer calls.
CDMA utilizes a spread-spectrum approach which typically facilitates deployment in dense urban areas where multi-pathing is an issue and results in fewer dropped calls. Furthermore, CDMA technology is more power efficient, thereby prolonging the standby and active battery life. One attractive feature of CDMA is that it offers a greater capacity for carrying information over typically limited bandwidth. Airwaves are usually divided into a limited number of different frequency bands by governing organizations (e.g., Federal Communications Commission (FCC) regulations). For example, limited segment of the airwaves are allocated for cellular usage. Due to the huge demand for cellular usage and the limited bandwidth that is available, getting a license from a governing organization to transmit on a particular frequency band is typically expensive. By increasing capacity, CDMA enables Personal Communications Services (PCS) providers to carry more users per channel and usually translates into greater utilization of the limited resources.
Increasingly, wireless digital applications are being used to access digital data (e.g., the Internet, intranet, multimedia, business data, etc.) at high speeds. With high speed wireless access, mobile users can obtain instant access to the Internet, business data (e.g., stock market quotes, sales reports, inventory information, price checks, customer data, emails, pages, etc.), and other real time data (e.g., traffic updates, weather information, sports news, etc.). One desirable goal is to provide cellular handsets, personal digital assistants, portable communications devices, etc. the ability to transmit and receive digital data as well as make conventional telephone calls. This desire has intensified efforts towards ever faster mobile data speeds to meet customer demands. Recent CDMA based 3G standards are proposing increased data rates and capabilities. With greater data is speeds, it is possible to provide even more data to more users.
FIG. 1 shows a typical prior art CDMA system. User signals (e.g., digitized voice signals or digital packetized data) are first modulated by a code which enables multiple users to share the same cell. The most commonly used code is known as a “Walsh” function. As stated above, one advantage of CDMA for personal communication services is its ability to accommodate many users on the same frequency at the same time. This is accomplished by assigning a specific “Walsh” code to each user. Only that particular code can demodulate the transmitted signal for that particular user. Since Walsh codes are orthogonal, users with different codes do not interfere with each other. Next, the signal is modulated by a pseudo-random number. This effectively serves to “spread” the transmitted signal across a wider spectrum. By spreading the signal out across a wider spectrum, the overall power of the transmitted signal can be boosted without exceeding the FCC regulations in any one channel. Finally, user signals of that cell are summed and modulated by a sinusoidal carrier to overcome antenna length requirements to transmit and receive baseband signals.
Communicating the information via different channels provides a variety of advantages in wireless protocols. However, it is often convenient to communicate and/or information in a single stream. Thus, information communicated by CDMA systems is often converted into other protocols (e.g., for further communication and/or processing of the information). In these situations it is often advantageous to have a single stream of information. For example, large quantities of information are sometimes converted from wireless systems to wired communication systems (e.g., FDDI, etc.) for bulk communication (e.g., between cells with significant geographic separation). It is also often necessary to convert information communicated in parallel (e.g., bits of information communicated on 32 separate channels) into a single stream (e.g., a 32 bit word).
It is also often desirable to be in communication with multiple devices simultaneously from the same transmitted data stream. For example, “mesh”, “peer-to-peer” or “ad-hoc” networks offer reliability and efficiency advantages over the “hub-and-spoke” network topology typical of most existing wireless cellular communication systems.